1. Field of the Invention
This invention relates to an optical switch comprising a directional coupler doped with an active ion and a method for optical switching using the same.
2. Related Background Art
Recently, many types of optical switches formed of various directional couplers have been proposed. For example, the possibility of optical switching by gain saturation-induced phase shift in semiconductor directional couplers was reported by J. M. Liu and C. Yeh (Appl. Phys. Lett. 50(23), Jun. 8, 1987.). According to their report, in a semiconductor directional coupler with optical gain, the refractive index in its semiconductor waveguides change with light injection at intensities close to the saturation intensity due to light-induced changes in the carrier density. This change in the refractive index is expected to induce the optical switching in the directional coupler.
However, even the possibility of optical switching by gain saturation-induced phase shift in optical directional couplers which are doped with rare earth ions having capability for optical amplification has not yet been reported.